The (so-called) "Security Images" are so popular.  Most internet
software use these in their registration screens to block robot programs
(which may register tons of fake member accounts).  Security images are
basically graphical CAPTCHAs (Completely Automated Public Turing Test to
Tell Computers and Humans Apart).  This module gives you a basic
interface to create such an image.  The final output is the actual
graphic data, the mime type of the graphic and the created random
string.  The module also has some "styles" that are used to create the
background (or foreground) of the image.
